Maker, Thomas Mercer, England, c. 1970's. 7"h x 4.5"diameter - movement, 8" x  8". Model of John Arnold style spring detent escapement.  Bi-metallic balance temperature compensation. Two hour duration. Mercer had made few of these models, probably less than 10 in the 1970's. Some had damascened plates, some polished as in this example.